For example, related art liquid discharging devices, such as ink jet printers, include a discharge head that discharges a liquid and a carriage that holds the discharge head and can reciprocate. When the carriage is disposed at a liquid discharge position, the liquid discharging device discharges the liquid from the discharge head onto a recording medium to print images or characters on the recording medium. A main liquid tank that stores a liquid therein is detachably mounted to a main body of the device. For example, a tube supply type and a station supply type are used to supply a liquid from the main liquid tank to the discharge head.
Japanese unexamined patent application publication No. H10-291300 (hereinafter called JP H10-291300) describes a related art tube-supply-type liquid discharging device. In the related art liquid discharging device, a main liquid tank mounted to a main body is connected to a discharge head by a tube at all times. When a liquid is discharged from the discharging head, the liquid stored in the main liquid tank is supplied to the discharge head through the tube.
Japanese unexamined patent application publication No. H02-111555 (hereinafter called JP H02-111555) describes a related art station-supply-type liquid discharging device. The related art liquid discharging device includes a sub liquid tank that is held by a carriage. When the carriage is disposed at a liquid discharge position, the sub liquid tank does not communicate with a main liquid tank, and the liquid in the sub liquid tank is supplied to the discharge head. Under a condition that the amount of liquid remaining in the sub liquid tank is less than or equal to a predetermined value, the carriage is moved to a liquid refill position that is different from the liquid discharge position to make the sub liquid tank communicate with the main liquid tank, thereby refill the sub liquid tank with the liquid stored in the main liquid tank.
As such, in the tube supply type, the liquid discharge operation and the liquid supply operation are performed at the same time, and in the station supply type, since a a space for arranging the tube is not provided, it is possible to reduce the overall size of a liquid discharging device.
However, the discharge head of the related art liquid discharging device includes discharge nozzles, pressure chambers that communicate with the discharge nozzles, and a pressure applying unit that applies a discharge pressure to the liquid in the pressure chambers (for example, a piezoelectric actuator or a heating element). A substrate having an integrated circuit for driving the pressure applying unit mounted thereon is provided on the carriage. In recent years, the number of driving channels has increased, and a driving frequency has increased, regardless of the liquid supply type, in order to meet the demands for high resolution and high printing speed. Accordingly, the amount of heat generated from the discharge head has increased due to an increase in the heat generated by the internal resistance of the integrated circuit. When the heat is accumulated, the temperature of liquid increases while the liquid passes through the vicinity of the integrated circuit, and the viscosity of the liquid varies, which results in a variation in the discharge amount of liquid or the discharge speed of liquid from the discharge nozzles corresponding to the applied discharge pressure. Therefore, printing accuracy is lowered. In order to solve this problem, a structure has been proposed in which a heat sink formed of, for example, a metal plate, which is provided in the carriage. However, in this case, it is necessary to increase the size of the heat sink as the amount of heat generated is increased. As a result, the overall size of a carriage increases.
JP H10-291300 also describes a related art device that cools around the discharge head. The related art cooling device includes a coolant reservoir that is provided in a main body of the liquid discharging device and stores a coolant, a coolant circulating path which connects an inlet of the coolant reservoir and an outlet of the coolant reservoir through which the coolant passes, and a pump that pressurizes the coolant in the coolant circulating path to circulate the coolant. In addition, a portion of the coolant circulating path passes around the discharge head. According in the related art cooling device, since the discharge head is water-cooled, there is no variation in the viscosity of liquid, and it is possible to prevent printing accuracy from being lowered. In addition, it is possible to avoid an increase in the size of a heat sink and thus prevent an increase in the size of a carriage.